Accelerating pump



1933 v J. scHwgrss 2,139,387

ACCELERATING PUMP Filed Dec. 5, 1935 JOSEPH SCHWEISS INVENTOR A TTORNE YPatented Dec. 6, 1938 UNITED STATES PATENT oFFicE ACCELERATING PUMPJoseph Schweiss, St. Louis, Mo., assignor to Carter CarburetorCorporation, St. Louis, Mo., a

corporation of Delaware l Application December 3, 1935 Serial No. 52,651

'1 Claim. (Cl. 309-33) This invention relates to piston or plungerdevices particularly adapted for use in carburetor pump chamber wall. Inother cases solid metal pistons have been provided and usually these areformed of the same kind of metal as the chamberwall or of metal having asimilar coefiicient of expansion in order toequalize thermal strains inthe piston and chamber 'due to frictionor the temperature changes of anasso: ciated engine, I

Whereleather pistons are used there is great difficulty in maintaininguniformityin the Size 3') and texture of the leather parts due to varia.tions in the hides from which the leathers are made and for otherreasons. A' leather piston, being absorbent, swells when immersed inliquid with the result that such a pistonyif fitted to its chamberwhensaturated, may not function proption with the chamber wall and partsmay be dissolved or washed away by the fluid'resulting 30 in loss ofcompression even though thepiston apparently fitstightly within itschamber] Solid metal pistons are subject to the objection.

of being rigid in contour and thus unable to yield so as to conform withthe shape of the chamber, particularly when the piston and chamber areworn or do not exactly fit together for any other reason. Such a pistonalso embodies a ing pumps, a clearance between'a solid metal pis- 7'.)ton and the chamber wall of aproxlmately .001

inch in excess of thenormal working clearance ordinarily results in lossof pressure and 'im-;

proper functioning of the carburetor, particularly during acceleration.Pistons of leather, even ter wearing properties than rigid pistons.

An object of the present invention is to provide a piston particularlyadapted for use in a carburetor accelerating pump, which will function60 satisfactorily for a substantially greater period of Carburetoraccelerating pumps have frequently erly when allowed to dry out. Leatherpistons also are subject to substantial wear due to fric u. thoughexpansible, do not have substantially betoperation than previous pistonsof thistype, and ordinarily for the lifeof the automobile on which thecarburetor is used.

Another object is to provide a metal piston adapted to function properlywithin wider clearance limitsthan previous metal pistons.

Another object is to provide a metal piston which is substantiallyeasier and cheaper to manufacture wlthin extremely close limits ofvariation than previous metal pistons.

Another object is to produce a piston capable of automatic expansion totake up its own wear. Another object is to provide a piston of the abovetype adapted to conform with a chamber wall which isworn or otherwiseout of shape so as to maintain a sealing fit therein. I

Another object is to provide a resilient. expansibleyandpliable metalpiston.

Another object is to providea new method of manufacturing metal pistons.

These objects and other more detailed objects hereafter appearing areattained by the structures illustrated in the accompanying drawing inwhich:

stem embodying the invention.

Figure 2 is a section taken on the longitudinal center line of thedevice in Figure 1.

Figure 3 is an end view of the piston disassembled from-the stem.

Figures 4 and 5 are exaggerated diagrammatic sections showing the pistonassembled with a pump chamber but under different operating conditions.

f Figure 6 is an exaggerated top view and section showing the novelpiston assembled with a cylinder worn out of round.

Figure 7 is a view similar toFig ure 6 but showing the cylinder wornevenly all around.

The embodiment illustrated in the figures comprises a piston rod or stem1 having an aperture 2 at one end for attachment to associated mechanismand a reduced portion 3 at the other end threaded for a nut 4. Mountedon the reduced end of stem l is an air dome member including acup-shaped portion 5 extending beyond nut 4 and a bushing portion 6directly receiving portion 3 of the stem. Secured between the upper endof bushing portionli which in effect forms ashouldered part ofthe stemstructure, and a shoulder 1 at the end of portion 3 of the stem is awasher 9 and'a piston member generally designated at Ill. The piston andstenimay be as;- sembled in any suitable manner, and the air domestructure may be varied as desired, or omitted.

Air dome portioni extends slightly within cupshaped piston member Illand serves as a protector for the free edge of the piston member. Asmall clearance is provided between the piston member and air domeportion 5 to permit flexing Figure 1 is aside View of a piston andpiston ill) ' during the application of pressure through stem I. Endwall Ii is flattened and the periphery of the piston skirt as describedhereafter. Pis-, ton member II is formed conveniently though notnecessarily, by the stamp drawing process from a piece of sheet aluminumof approximately .006 inch thickness and comprises a disk-like end wallII and a cylindrical side wall portion forming a skirt I 2. The side andend wall portions are preferably Joined by a fillet as at It and the endwall portion is inclined slightly outwardly from the apertured centerthereof (Fig. ures 2 and 4). In the assembled device, the clampingwasher I and bushing portion. 6 are drawn together tightly against theflattened center portion of the generally dome-like or frustoconical endwall of the piston.

The above described shaping of the piston side and end walls is readilyattained by the stamp drawing process in which the 'sheetmetal is forcedinto a cylindrical die, the re-shaping of the metal under pressureresulting in slight bowing or "cupping in the disk-like center portionof the blank which forms the end wall of the cup. Where thin resilientmetal is used, as in the present case, the end wall forms, in effect, aflexible diaphragm and the offset center portion thereof may be flexedunder axial pressure and upon release of the pressurewill re-assume itsoriginal position provided the flexing does not exceed the elastic limitof the material. During inward flexing, the metal yields in a directionparallel to its surface and the peripheral portion thereof is expanded.w

In the piston described above, substantially the entire end wall ii ofthe cup including the fillet I! may flex, as described, during theapplication of pressure coaxially of stem l, or only a portion thereofmay be cupped so as to function in this manner. The side wall or skirtof the piston or a portion thereof, preferably, though not necessarily,is inclined slightly outwardly from the end wall po on as at It and thisshaping also is readily fo ed by the stamp drawing process whereresilient metal is used.

Figures 4 and 5 illustrate on a greatly exaggerated scale, the manner inwhich the novel piston functions-to seal a cylinder or chamber. InFigure 4 the piston end wall is contracted and cupped, as is the casewhensubstantially no pressure is applied thereto through stem l. A

portion of skirt I2 is shown as spaced from the chamber wall H.Inpractice only very. slight clearance is provided" between the skirtand chamber wall and the skirt throughout its depth may engage thechamber wall.

Figure 5 illustrates the condition of the parts thereof expanded towardsthe chamber wall, resulting in the application of pressure transverselyagainst the chamber wall through piston skirt it. The skirt is thusforcedagainst the chamber wall and into sealing engagement therewith.

The skirt, being. laterally flexible, can yield to conform with thecrossv sectional shape of the chamber wall. Figure 6 illustrates, ingreat exaggeration, a condition in which the piston chamber isnon-circular in cross section due to wear. or for any other reason, thepiston skirt being distorted correspondingly. Such a condition may existdue to production the chamber is worn by use.

In Figure '1, the chamber, while cylindrical, is

tolerances or after aisassr slightly larger all around than the piston.In this case, the piston expands uniformly all around when pressure isapplied to stem I to force the'piston skirt into sealing engagement notnecessarily, formed of aluminum, or other material which has a great rcoefficient of thermal expansion than the chamber wall, ordinarilybrass. in carburetor accelerating pumps, so that the seal will beimproved when the piston becomes heated. The piston will functionpropcrly for a period of time longer than non-flexing pistons, eventhough formed of softer material than the chamber wall, or vice versa,due to its ability to'expand and to conform with a noncircular chamber.Aluminum is a satisfactory material for forming the piston due to itsresistance to corrosion, lightness, strength, resilience, andworkability.

The piston need expand or distort only a very small amount and no actualexpansion may occur where the piston closely fits within its chamber.The pressure developed in a carburetor accelerating pumpduring eachstroke of the piston is not very great, but this pressure, in additionto the friction between the piston skirt and chamber wall,'oflerssufflcient resistance to forces applied through the piston stem toinsure slight flexing of the piston end wall provided the cupping orbowing of this portion of the piston is not too great.

The novel sheet metal piston has important advantages .even though theend wall portion thereof is formed flat instead of being slightlycupped. The yielding skirt portion will readily conform with cylinderwall irregularities or imperfections and may be easily stretched orshaped,

particularly at its freeedge by a suitable tool or instrument. It hasbeen found that the pressure developed by the piston and consequentlythe rate of ejection of fuel from a carburetor accelerating pump inwhich the piston is used may be increased by merely expanding the pistonskirt. This in particular, facilitates servicing of used carburetors.The facility and cheapness of manufacture, durability and uniformity ofsuch a piston also constitute distinct advantages not attained in othertypes of metal and leather pistons.

Obviously the shaping and proportion of various parts of the illustratedembodiment may be varied and certain parts may be eliminated withoutdeparting from the spirit of the invention. Also the piston may beformed by a process other than stamp drawing. The exclusive use of allsuch modifications as come within the scope of the appended claims iscontemplated. I claim:

A piston comprising a thin sheet metal cup having an annular rim with asubstantially smooth surface both inside and out, at least a portion ofthe end wall of the cup being substantially of frusto-conical shapewhereby pressure exerted at the center of said end wall in one directionwill tend to cause expansion of the outer wall of the cup.

JOSEPH SCHWEISS.

